Water Meter Going Backward

[Mr_David]

Lets say your water pressure is 60 psi.
You put a pressure gauge on a faucet or laundry valve in the house and turn on any other fixture you will normally get about a 5 psi drop in pressure.
The same if you open a yard spigot on the other meter. Some of that water in the house system will flow back to the opened yard spigot thus causing a reverse meter flow.
The large volume of water in the water heater helps feed that back flow. Makes sense to me. Check valve after the meter would probably work and easier to install
Having 2 meters , one for yard water and one for house water so they can bill you for sewer based on house water used is new to me but seems to be a good idea.

[mooseye]

I am assuming that the supply is coming up thru the tee then going left and right thru the meters. If this is correct, a check valve installed where the red arrow is will solve the problem. I can't believe 2 professional plumbers could not see the problem there.
It is very easy to see how opening the outdoor line would create a pressure drop and allow the water in the house supply to flow back, especially if the home water is mostly at a higher elevation.
It is hard to understand how there could be enough backflow for the utility co. to notice it. Even if it drained the whole system including the water heater, it should flow back and refill the system when the outdoor flow is stopped, thus counteracting any reversal of the meter.
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[barnabas1969]

I have to agree about the galvanized T connected to brass fittings AND about the metal clamps on the plastic pipe. Just plain dumb to use iron and brass/copper together... and it is against every CPVC manufacturer's installation instructions to use metal hangers/clamps on CPVC pipe.

As for the reverse flow... if you have an expansion tank on your water heater or somewhere else in the house, that would completely explain the backflow problem. You should definitely have a check valve.

[Plumber001]

Originally Posted by tranelch

Shortly after finishing construction on our new home, the utilities company called to question our meter reading. Through experimentation with the department of public works, we discovered that sometimes when the outdoor spigots (water only meter) were running, the indoor meter (water and sewer) would turn backward. We never had air in the pipes, so we concluded that the meters were installed so close to the supply "T" (see attached photo), the turbulence was causing the meter to turn backward (in addition, if water was actually flowing backward, it would have to go back through the meter and would cancel out the backward flow). When I relayed our conclusion to our plumber, he responded that:


That just didn't make sense to me (the negative static pressure comment, if I understand it correctly, would suggest that the head pressure is pushing harder than the supply to the house when the outdoor spigots are running--we know that water is not flowing out through the meter), and I was not convinced that paying to install a check valve on the supply before the "T" would solve our problem. I then asked another local plumber to have a look at it. He agreed that the meters were too close to the "T"

I am wondering if the unbiased folks on this forum could break the tie and share there opinion on what is likely causing our meter to run backward.

Thanks in advance,
Chris

I'm guessing you have a expansion tank on your water heater. When you use the outside spigot it will draw from both sorces untill the pressure equilizes.

[barnabas1969]

Originally Posted by Plumber001

I'm guessing you have a expansion tank on your water heater. When you use the outside spigot it will draw from both sorces untill the pressure equilizes.

I completely agree. I had a similar issue. My issue was that there was no check valve at the meter, so surges in the city mains would cause water to alternately flow in and out of my meter. The expansion tank contains air that can be compressed, unlike water which cannot. This causes the in/out flow when the city mains change pressure. The city water pressure varies constantly by a few PSI, I assume due to fluctuations in demand.

The problem is that most meters aren't designed to run backward and don't measure reverse water flow correctly, so it was registering more in-flow than out-flow... resulting in higher water bills.

The city where I live has an on-going project to install check valves in older neighborhoods, but I didn't wait... I installed one myself. It fixed the problem immediately, and my water bill went down about $10-20 per month! That paid for the check valve in a hurry.